Mismatched Tyres

Tony Wilson · Post by **Tony Wilson** » Mon May 07, 2001 6:27 pm

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Tony Wilson · Post by **Tony Wilson** » Mon May 07, 2001 6:49 pm

My '89 MX 5 has near new 195/50 R15 tyres on the front and worn out
205/50 VR15 tyres on the rear. Is their any likely reason why a previous
owner would have fitted different tyres to the rear in the past
?(modified suspension etc.) The car handling has always seemed ok but
then I have nothing to compare it with. Unless your comments convince me
otherwise, I intend fitting new 195/50 R15 to the rear to keep all the
tyres the same. Your advice or comments will be appreciated. Thanks Tony

Ray · Post by **Ray** » Mon May 07, 2001 8:07 pm

Hi Tony
People do all sorts of strange things with tyres as people often put a cheap price
on their own lives and everyone else, this discussion often comes up regarding tyres,
do you know the width of your wheels? in my opinion 205's are a waste of money if
your car has a near stock engine, even if the suspension is modified, as they will
never get to the correct operating temperature, (yes even modern day road tyres need
to get warm), 195's would be my choice on 15ins wheels, and you are also correct
to make them all the same make, there are a lot of people on this list that will
recomend a good brand for you, me, i use Yokohama AVS, excellent in the wet and dry.

Ray

<html><DIV>My '89 MX 5 has near new 195/50 R15 tyres on the front and worn out 205/50
VR15 tyres on the rear.</DIV>
<DIV> </DIV>
<DIV>Is their any likely reason why a previous owner would have fitted different
tyres to the rear in the past ?(modified suspension etc.) The car handling has always
seemed ok but then I have nothing to compare it with.</DIV>
<DIV> </DIV>
<DIV>Unless your comments convince me otherwise, I intend fitting new 195/50 R15
to the rear to keep all the tyres the same.</DIV>
<DIV> </DIV>
<DIV>Your advice or comments will be appreciated.</DIV>
<DIV> </DIV>
<DIV>Thanks</DIV>
<DIV> </DIV>
<DIV>Tony</DIV>
<DIV> </DIV>
<DIV> </DIV><br clear=all><hr>Get Your Private, Free E-mail from MSN Hotmail at <a
href="http://www.hotmail.com">http://www.hotmail.com</a>.<br></p></html>

Colin · Post by **Colin** » Mon May 07, 2001 8:33 pm

Hi, Tony

I agree with Ray completely about mismatched tyres.
You don't mention the wheel width.
ie: 15 x 6 = 195x50 tyre size
15x6.5=195x50(perfect)
15x7.0=205.45

As a general guide... 6 inch wide rim equals 185 wide tyre
6.5 inch wide rim equals 195 wide tyre
7.0 inch wide rim equals 205 wide tyre
Clearly the profile needs to reduce to effect a close to nil change in
overall circumference.
It is incredibly important on Alignment supersensitive cars to retain the
original 'scrub radius
on mx5's this means a 45mm offset with a close to original circumference.
To clarify... my MX 1994 with 14x6x45 wheels = perfect fit 185x60x14 tyre
my MX 1994 with 16x6.5x45 wheels = (almost) perfect
205x45x16 tyre (2.3% out)
The contact patch between these tyres has changed from 'longitudinal' to
latitudinal.
I can add to the discussion of why this is important if you would like.
Finally... I was once asked why I had spent so much on a Crash Helmet.
I gave an answer that I believe to be true.. I can't think the
amount of money my head is worth! (quiet Fletcher!)
So it is true of tyres.
If price is an issue. Please contact me.
Oops another epistle...
pleased to add to the discussion

Colin

Tony Wilson · Post by **Tony Wilson** » Tue May 08, 2001 8:05 am

Colin / Ray

Thanks for taking the time to reply.

The rim width is 7 inches - I take it then that 205's are the correct
tyre ?

Tony

Ray · Post by **Ray** » Tue May 08, 2001 9:36 am

Hi Tony
yes you are correct, 205x50, Colin got it in one superbly, if your 195's are good

most tyre shops will do a deal for you on them, and pick a good known brand performance

tyre that suits a MX5, and stretch your funds to the limit in doing it, your car

will love you for it, then get a good wheel alignment done front and back.
Ray

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Post by **zorruno** » Tue May 08, 2001 11:14 am

An issue that I think has been implied here but not mentioned is that IMO
the reason for going for same tyres all round (size brand and model) and
without debating the merits of width/brand etc is that the MX5 was designed
to be a balanced car.

As has been said before about suspension, anything you do to one end should
be done to the other, unless you are intending to upset the balance slightly
and sway towards over/understeer/turn-in etc.

Larger more powerful RWD cars often have wider tyres on the rear to provide
traction under power without upsetting the ability to steer

These are
also usually unbalanced cars.

195/50 15 is also closer to a the accepted stock circumference than 205/50,
but not by much. I've run 195s and 205s on 16x7" rim, and prefer 205s. I
had 225s on my last car (MX6), but went back to 205s for a number of
reasons. Actually last time I checked, a 195/45 was closer to stock
circumference for a 16" rim than than a 205/45, but they are all only within
a few %

I do feel though that your first area of "as much as you can" spending for
an MX5 should be on tyres.

H

Ray · Post by **Ray** » Tue May 08, 2001 2:59 pm

zorruno is quite correct as to the balance of an MX5, so i will add that if anybody
now think that they have the wrong tyres on their 15x7 rims, it is quite acceptable
to put 195x50 on these rims, and this size would still be my choice on an unmodified
MX5, on Mazdaspeeds supercharged MX5 (Miata Mag 98-1) they used 195x50 on their 15x7,
and as zorruno said he prefered the 205's after trying the 195 size, in fact 205's
are the size i use on my 16x7.5 rims, and i have a lot more HP than most but they
still take 5ks to get to a working temperature where they operate correctly for some,
er!!! spirited driving.
I hope this is not to confusing for the first time MX5 driver.
Ray

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